This invention relates to a switch which is sensitive to a pulse of charge imparted to a conductive sensor, as by touching it with the hand of a person, and therefore can be used to control the operation of a variety of appliances.
Touch-sensitive electronic switches which do not utilize a user-activated bending of a spring to effect an electrical contact, are used frequently for the operation of elevators, etc. While the application of this type of electronic switch has been previously attempted for the control of lamps, electrical motor-driven appliances, etc., the switches have not found wide usage for control of those appliances, due to a number of problems.
Charge sensitive electronic switches commonly use silicon controlled rectifiers or silicon controlled switches in the heavy current load circuit. Excess load, i.e., high current in excess of the design maximum of the semi-conductor switch frequently destroys the switch. Consequently the use of a silicon controlled switch to control a lamp designed for a maximum 60 watt light bulb, could cause destruction of the silicon controlled switch if, for instance, a 150 watt light bulb is inserted into the lamp socket, unless the silicon controlled switch has sufficient overcurrent capacity to handle, on a continuing basis, particular overcurrents. However, temporary short circuits within the light bulb, or the placement of still higher wattage light bulbs in the lamp socket by the consumer, could cause failure of the silicon controlled switch, even with a reasonable amount of overcurrent capacity.
In addition, when a user touches a "touch plate" sensor by merely brushing the hand over it, a rapid sequence of charge pulses may be imparted to the switch, which could cause the light bulb to flicker on and off, in a lamp, giving the impression of a non-positive and unreliable contact closure. Even in the absence of the above sequence of charge pulses, a user might sequentially turn the switch on and off on purpose very rapidly, possibly causing damage to the appliance due to too frequent current surges.
Furthermore, it has been found that persons of various body sizes will impart various amounts of charge to a sensor touch plate. A child may carry a very small amount of charge, while a tall person may carry a significantly larger charge. A switch which has been designed to be sensitive to the charge of a child, may be so sensitive as to pick up stray charges present in the air on a dry winter day, causing operation of the switch-operated appliance in a sporadic and unreliable manner.
It is believed that due to the aforenoted problems, charge-operated electronic switches have not found wide use to control appliances which must be operated by children as well as adults (as in a table lamp), or with appliances which are generally used by the consumer in an uncontrolled environment.
The present invention contains a unique structure whereby the aforenoted problems with prior art switches are overcome. The present charge-operated switch contains an overcurrent detector, which senses excessive current which would otherwise damage the silicon controlled switch, and takes action to shut the current off. The present charge-sensitive switch can therefor be used with an appliance which is subject to user-induced overload, and be immune from overload current-draw damage.
The present invention also contains means for accepting charge pulses following a first charge pulse only after a predetermined interval has lapsed. Accordingly, if a number of charge pulses are imparted to the switch sensor in rapid succession, only the first will be sensed, and the appliance turned on or off. After the aforenoted time period, a further pulse will be accepted. Accordingly, the aforenoted flickering, unstable or indeterminate operation of the light bulb is avoided and the appliance will be turned on or off with certainty and reliability.
According to the present invention, as well, a charge pulse applied to the same sensor will turn the switch on or off, in successive steps. Prior art switches in the main have required two touch plates, or a mechanical reset button elsewhere in the circuit.
A feature of one embodiment of the invention is the provision of a switch which can sequentially turn on a number of circuits. This embodiment can be used in the operation of multi-filament (e.g. three way) light bulbs, or be used to control apparatus utilizing sequentially operated activation.
In addition, the present invention can have its sensitivity varied at will. Preferably, the sensitivity is prefixed at a level which will allow it to be operated by a variety of charge pulses, for instance from a small-bodied child, to a large adult.
However, it should be noted that the sensitivity of the switch can be set so high, that a charge carrying person only approaching near the charge sensor can operate the switch. Accordingly, there is substantial utility of the invention in the provision of charge sensors encompassing the metal frame of a storage safe, or a wire behind the frame of valuable pictures in an art gallery, etc. The silicon controlled switch can be used in an alarm circuit, whereby too-near approach of a visitor to the art gallery, to a wired picture will set off an alarm and summon a guard. Similarly, the near approach of a burglar to a suitably wired safe can provide an alarm, as noted above.
It should be noted that the term "silicon controlled switch" is intended to be used generically, and includes devices such as silicon controlled rectifiers, or other electronic switches. The use of the term "switches" is intended to be generic to silicon controlled switches, as noted above, as well as relays and other electrically operated switching structures, which provide a heavy current switched path upon reception of an input operation signal.